Natural and Synthetic Diamonds
Natural diamonds are created by geological processes. Natural diamonds have ages from 1 to 3.5 billion years, were mostly formed at depths of 150Ė250 km in the mantle and have been carried to the surface by volcanic eruptions. The value of a diamond as a gem is determined by its carat (its mass in carats where one carat is equal to 0.2 g), clarity, color and cut, known informally as four Cs. More than half of mined diamonds donít have gem-quality and are used in industry at where diamonds are valued for their exceptional hardness and thermal conductivity.
Synthetic diamonds also known as lab-grown or cultivated diamonds are created artificially by using mainly HPHT (high pressure high temperature) and CVD (chemical vapor deposition) processes where resultant diamonds may be named HPHT and CVD diamonds respectively. HPHT method, the original method of production of synthetic diamonds, creates diamonds by using high pressures (like 5 GPa) and high temperatures like (1800 K). CVD diamonds also known as diamonds by CVD or low-pressure diamonds are formed as crystals or as films from various gaseous hydrocarbons or other organic molecules in the presence of activated, atomic hydrogen. Hydrogen plays a fundamental role in CVD method by selectively etching off non-diamond carbon.
Recently, about 150 million carats natural diamonds are mined annually. The global annual production of synthetic diamonds mostly used in industry is currently about 4-5 billion carats (800-1000 tonnes) where about 90% of this amount is produced in China. 4-5 million carats of annually-produced synthetic diamonds has gem-quality. While cut diamonds with natural origin can have masses as high as about 500 carats as in Golden Jubilee diamond (545.67 carat) and Cullinan I (530.4 carat), lab-grown gem-quality cut diamonds with masses above 10 carat are among records.
It may also be interesting to know that in 2011, one-carat diamonds were traded from 200 to 25000 USD depending on their cut, clarity and color. Also, in 2011, the one-carat highest-quality diamond was traded for 25000 USD while the 4-carat highest-quality diamond was traded for 500,000 USD. In addition, in a typical diamond mine, diamonds lighter than 0.1 carat respectively occupy 50% of volume and 20% of value of all mined diamonds while diamonds heavier than 2 carats respectively occupy 5% of volume and 50% of value of all diamonds.† (Source: Diamond Industry Report 2011, Bain & Company, Inc.)